Due to the requirement of tires having higher fuel efficiency, a rubber composition comprising silica is now used for not only a tread, but also various components of tire. However, since silica has a hydrophilic silanol group on its surface, the affinity thereof with a rubber component (particularly, a natural rubber, a butadiene rubber and a styrene butadiene rubber which are often used for a component of tire, and the like) is low compared to that of carbon black, and there is a problem that abrasion resistance and mechanical strength (tension strength and elongation at break) are inferior.
As a method for improvement by solving such problem, a method of enhancing a reaction between a rubber component and silica by use of a coupling agent is known. However, usual coupling agents have a problem that functional groups thereof react to each other before being brought into reaction with silica and coagulate, and there was a limit in an effect of dispersing silica. Also, a method of introducing a modifier which reacts with silica into a rubber component to improve reactivity between the rubber component and silica is known. However, these methods can stand further improvement in achieving both processability and fuel efficiency.
Moreover, recently, the requirement for abrasion resistance has been getting stronger in addition to fuel efficiency from the viewpoint of natural resources protection. As a method of improving abrasion resistance, a method of using particulate silica with high reinforcing effect and the like is known. However, particulate silica is generally very difficult to be dispersed in a rubber composition and there are problems that it cannot disperse enough and a coagulated mass remains and thus cannot improve abrasion resistance and mechanical strength, or even worsen these properties in some cases.
In Patent Document 1, a technique of improving fuel efficiency, wet grip performance and processability of a rubber composition in a good balance by a combined use of a specified silane coupling agent 1 and a specified silane coupling agent 2 is disclosed. However, there is still room for improvement in achieving both wet grip performance and fuel efficiency. Further, improvement of abrasion resistance is not considered.
Moreover, in the case where a large amount of silica is used for improvement of fuel efficiency, an electrical resistance of tire becomes high and thus for example, fuel may catch fire with a spark of static electricity at fuel supply of vehicle, that is to say, there is a problem in safety at use.
In Patent Document 2, a tire in which rolling resistance is reduced without reducing electrical conductivity of tire by providing a conductive membrane at a tread portion and a sidewall portion is described. However, since this technique complicates a process of tire production and has a problem in cost, a rubber composition which can easily improve fuel efficiency and electrical conductivity in a good balance is required.